Polyphenylene ether/thermoplastic elastomer block copolymer blends for adhesives and sealants

ABSTRACT

The present invention provides a method for making a method for making high service temperature rubber compound, hot melt adhesive or sealant compositions by combining a polyphenylene ether resin with an elastomeric block copolymer of a vinyl aromatic hydrocarbon and a conjugated diene, which comprises (a) making a masterbatch of 2 to 50 phr of a polyphenylene ether having an intrinsic viscosity of 0.3 deciliters per gram or more and 100 phr of said block copolymer by extruding them together with 2 to 30 phr of an endblock compatible resin, and (b) optionally mixing the masterbatch with more of the block copolymer.

BACKGROUND OF THE INVENTION

The present invention relates to high service temperature blockcopolymers which contain polyphenylene ether resins and block copolymersof vinyl aromatic hydrocarbons and conjugated dienes. More particularly,the present invention relates to a method for making improved highservice temperature block copolymer blends which can be used for rubbercompounds and hot melt adhesive and sealant compositions utilizingpolyphenylene ether resins and such elastomeric block copolymers.

Hot melt adhesive compositions containing polyphenylene ether resins andblock copolymers of vinyl aromatic hydrocarbons and conjugated dienesare well known. In U.S. Pat. Nos. 4,104,323 and 4,141,876, the patenteedescribes such hot melt adhesive compositions containing low molecularweight polyphenylene ether (PPE) resins. Such low molecular weight PPEshave a molecular weight as described by intrinsic viscosity of less than0.3 deciliters per gram. The patents also describe blends of such blockcopolymers and PPEs with higher viscosities, i.e. 0.3 deciliters pergram or more and show that the blends with the lower molecular weightPPEs are superior to those using the higher molecular weight PPEs.

In commercial practice, it has proved difficult to use either the blendswith the high molecular weight PPE or the low molecular weight PPE inadhesive and sealant formulations. It has proved very difficult toadequately mix the PPEs with the block copolymers in commercialequipment. This is most likely due to the limitations of the equipmentwhich is most often used by formulators who are interested in making hotmelt adhesives or sealants with these materials. Such compounders andformulators normally use lower viscosity materials than PPE and thus donot require high intensity mixing apparatus.

Therefore, it would be very advantageous if a way were found to permitthese high service temperature adhesive and sealant compositions to bemade in the currently commercially used low intensity mixing equipmentsuch as Sigma Blade mixers. The present invention provides such a methodand allows the formulator or compounder to achieve a very. goodcompatible mixture of these materials while using the lower cost mixingmethods which are currently being used commercially today.

The aforementioned U.S. Pat. Nos. 4,104,323 and 4,141,876 describe theadvantages of utilizing lower molecular weight PPEs, i.e. the ability toachieve high service temperatures in the blends while avoiding the highviscosity which is a characteristic of the higher molecular weight PPEs.The lower molecular weight PPEs are difficult to make commercially.Therefore, it would be an advantage to find a way to make a lowerviscosity high service temperature blend using the higher molecularweight PPEs. The present invention also provides such a method.

SUMMARY OF THE INVENTION

The present invention provides a method for making high servicetemperature rubber compounds and hot melt adhesive/sealant compositionsby combining a polyphenylene ether resin with an elastomeric blockcopolymer of a vinyl aromatic hydrocarbon and a conjugated diene. Themethod comprises first making a masterbatch of 2 to 50 phr, preferably 5to 30, of a polyphenylene ether resin having an intrinsic viscosity (IV)of 0.3 deciliters per gram or more and 100 phr of said block copolymerby extruding them together with 2 to 30 phr of an endblock compatibleresin. This masterbatch can be used by itself or compounded further withother ingredients to form adhesive, sealants or rubber compounds. Thismethod is also advantageously utilized with a polyphenylene ether havingan intrinsic viscosity of less than 0.3 deciliters per gram. If the lowmolecular weight PPE is used, the endblock resin is not necessary. Phris parts by weight per 100 parts rubber wherein "rubber" refers to theblock copolymer.

The present invention also encompasses the masterbatch described aboveand the product of the process described above. The product utilizingthe lower molecular weight PPE is characterized by lower viscosity whichis important for rubber compounds and adhesives/sealants. Surprisingly,the masterbatch product made with the higher molecular weight PPE andthe endblock compatible resin exhibits a viscosity and servicetemperature which is comparable and almost equivalent to that of thecomposition made using the lower molecular weight PPE. This isadvantageous because the desired result can be achieved without havingto use the difficult to manufacture lower molecular weight PPE. Also,when the masterbatch is let down into a typical sealant formulation,sealant with the endblock resin/PPE blend, it performs as well as theformulation with the pure 0.4 IV PPE indicating there is betterutilization of the high temperature PPE component.

DETAILED DESCRIPTION OF THE INVENTION

The block copolymers which form the base polymer for the adhesive andsealant compositions of the present invention are thermoplasticelastomers which are block copolymers of vinyl aromatic hydrocarbons andconjugated dienes. The polymers have to have at least two vinyl aromatichydrocarbon blocks and at least one elastomeric conjugated diene block.The number of blocks in the block copolymers is not of specialimportance and the macromolecular configuration may be linear, graft,radial or star, depending upon the method by which the block copolymeris formed. Typical block copolymers of the most simple configurationwould have the structure polystyrene-polyisoprene-polystyrene orpolystyrene-polybutadiene-polystyrene. It is highly preferred that theblock copolymers be hydrogenated because it allows more flexibility inmixing conditions because higher temperatures can be used. A typicalradial polymer would comprise one in which the diene block has three ormore branches and the tip of each branch is connected to a polystyreneblock. The branches are connected together or coupled to a couplingagent in the center. Star polymers are similar to radial polymers exceptthat they have many more arms and the coupling agent is usually amultifunctional material such as divinyl benzene. Further descriptionsof such block copolymers and methods for making them are taught in U.S.Pat. Nos. 3,231,635, 3,265,765, 3,322,856, 4,096,203, 4,391,949, and5,104,921, which are herein incorporated by reference.

The preferred vinyl aromatic hydrocarbon used in these block copolymersis styrene. Other useful vinyl aromatic hydrocarbons includeα-methylstyrene, various alkyl-substituted styrenes, alkoxy-substitutedstyrenes, vinyl napthalene, vinyl toluene and the like. The preferredconjugated dienes are butadiene and isoprene. Other dienes which may beused include piperylene, methylpentadiene, phenylbutadiene,3,4-dimethyl-1,3-hexadiene, 4,5-diethyl-1,3-octadiene and the like.Preferably, those conjugated dienes containing four to eight carbonatoms. The diene segment of the block copolymer also can be hydrogenatedto eliminate the double bonds.

The molecular weights of these block copolymers vary from as little as10,000 up to as much as 2,000,000. The molecular weights of such blockcopolymers are usually and most advantageously determined as the peakmolecular weight as determined by gel permeation chromatography, a wellknown and well documented method described in many patents includingU.S. Pat. Nos. 5,229,464 and 5,247,026, which are herein incorporated byreference. For use in rubber compounds (compounds containing the blockcopolymers and polyolefins, such as polypropylene and polyethylene,and/or other thermoplastics, such as nylon, polycarbonate, etc., andother ingredients such as plasticizers and fillers) and adhesive andsealant compositions utilizing PPE resins, it is preferred that themolecular weight of these block copolymers (as determined by GelPermeation Chromatography-peak molecular weight) range from 30,000 to1,500,000 with the molecular weight of the vinyl aromatic hydrocarbonblocks ranging from 5000 to 30,000 and the molecular weight of theconjugated diene blocks ranging from 20,000 to 150,000.

The low molecular weight polyphenylene ether resins are low molecularweight resins having an intrinsic viscosity of less than 0.3 decilitersper gram, when measured in solution in chloroform at 30° C. The highermolecular weight resins described according to the present inventionhave an intrinsic viscosity of 0.3 deciliters per gram or more.

The polyphenylene ether resin is preferably one which is comprised ofthe formula: ##STR1## wherein the oxygen ether atom of one of the unitsis connected to the benzene nucleus of the next adjoining unit, n is apositive integer and each Q is a monovalent substituent selected fromthe group consisting of hydrogen, halogen, hydrocarbon radicals free ofa tertiary α-carbon atom, halohydrocarbon radicals having at least twocarbon atoms between the halogen atom and the phenyl nucleus,hydrocarbonoxy radicals and halohydrocarbonoxy radicals having at leasttwo carbon atoms between the halogen atom and the phenyl nucleus.

For purposes of the present invention, an especially preferred family ofpolyphenylene ethers includes those having alkyl substitution in the twopositions ortho to the oxygen ether atom, i.e., those of the formulawherein each Q is alkyl, most preferably having from one to four carbonatoms. The most preferred polyphenylene ether resin for the purposes ofthis invention is poly(2,6-dimethyl-1,4-phenylene)ether.

In general, the polyphenylene ether resins of this invention can beprepared by the following procedures fully described in U.S. Pat. Nos.3,306,874 and 3,257,375, which are herein incorporated by reference. Thepolyphenylene ethers are self-condensation products of monohydricmonocyclic phenols typically produced by reacting the phenols in thepresence of a complexing agent or complex metal, e.g., copper catalyst.In general, the molecular weight will be controlled by the reaction timewith longer times providing a higher average number of repeatingstructural units. For low molecular weight PPE, at some point before anintrinsic viscosity of 0.3 deciliters per gram, is obtained, thereaction is terminated. Obviously, for higher molecular weight PPE, thereaction is continued until the desired molecular weight is achieved.Termination can be brought about by the use of conventional means. Forinstance, in the case of reaction systems which make use of complexmetal catalysts, the polymerization reaction can be terminated by addingan acid, e.g., hydrochloric or sulfuric acid, or the like, or a base,e.g., lime sodium hydroxide, potassium hydroxide, and the like, or theproduct is separated from the catalyst by filtration, precipitation orother suitable means.

The endblock compatible resin is a resin which is compatible with thepolymer block which is normally on the end of the block copolymers ofthe present invention, i.e., the vinyl aromatic hydrocarbon block. Suchendblock compatible resins are often used as reinforcing agents.Normally, these resins should have a ring and ball softening pointbetween 80° C. and 150° C. although mixtures of aromatic resins havinghigh mid low softening points may also be used. Useful resins includecoumarone-indene resins, poly alpha methyl styrene, polystyrene resins,vinyl toluene-α-methyl styrene copolymers and polyindene resins.

Examples of aromatic resins useful in the formulations of the presentinvention are AMOCO® 18 series resins, which are composed of alphamethyl styrene (AMOCO), Kristalex® series resins, which are composed ofalpha methyl styrene (HERCULES), PICCOTEX® Series resins, which arecomposed of alpha methyl styrene and vinyl toluene (HERCULES), NEVCHEM®(NEVILLE) and PICCO 6000 (HERCULES) series resins, which are composed ofaromatic hydrocarbons, CUMAR® series resins and CUMAR LX-509 (NEVILLE),which are composed of coumarone-indene, PICCOVAR® AP series resins(HERCULES), which are composed of alkyl aryl species, PICCOVAR® 130(HERCULES), which is an alkyl aromatic poly indene resin, and ENDEX® 155(HERCULES), a resin derived by copolymerization of pure aromaticmonomers.

The method of the present invention provides high service temperaturerubber compounds and hot melt adhesive/sealant compositions. Forexample, the method involves making a masterbatch of 20 phr of apolyphenylene ether having an intrinsic: viscosity of 0.4 deciliters pergram and 100 phr of a block copolymer of a vinyl aromatic hydrocarbonand a conjugated diene by extruding the two together with 10 phr of theendblock compatible resin. The final step of the process for adhesivesand sealants is mixing the masterbatch with 90 to 250 phr of atackifying resin and, optionally, more of the block copolymer to formthe adhesive or sealant composition. The masterbatch could also becombined with polyolefin resins such as polypropylenes or polyethyleneplasticizers and fillers to form rubber compounds.

It is important to note that the masterbatch method is also advantageousto use when a low molecular weight PPE, i.e., a PPE having an intrinsicviscosity of less than 0.3 deciliters per gram, is used. The masterbatchis made in the same manner but the endblock compatible resin is notnecessary. This blend with the lower molecular weight PPE has thecharacteristics of high service temperatures without the increase inviscosity that is normally associated with the use of the highermolecular weight PPE. Quite surprisingly, when the masterbatch method isused with a high molecular weight PPE and an endblock compatible resin,the service temperatures and the viscosities of such masterbatch blendsare comparable to and almost equivalent to the service temperatures andviscosities of blends using the lower molecular weight PPE.

The masterbatch is made by introducing the PPE and the block copolymerinto a Berstroff twin screw extruder, for example, and running themthrough the extruder at a temperature of about 250° C. to about 310° C.The same mixing conditions can be used when an endblock resin is addedwith the advantage being lower viscosity.

The key advantage of the present invention is providing a formulationwhich has a higher service temperature than formulations utilizing theblock copolymers alone. The addition of the PPE increases the servicetemperature as well as the viscosity. The use of these formulationshelps to improve the heat distortion properties of the thermoplasticelastomers and make them more useful in automotive, wire and cable, andother applications involving high temperatures.

The masterbatch of the present invention is formed under high shearconditions in an extruder. This allows the production of a very wellmixed and very compatible blend of the two or three components involved.The extremely well mixed and compatible condition of the masterbatchmakes it possible to take the masterbatch and mix it with otherformulating ingredients such as resins, plasticizers, and polyolefins instandard commercial mixing equipment which is much lower shear than anextruder (such as a Sigma Blade mixer or Banbury mixer) and stillproduce very good compositions whether rubber compounds or adhesives orsealants.

It may be necessary to add a different kind of adhesion promoting ortackifying resin that is compatible with a polymer. A common tackifyingresin is a dieneolefin copolymer of piperylene and 2-methyl-2-butenehaving a softening point of about 95° C. This resin is availablecommercially under the tradename WINGTACK® 95 and is prepared by thecationic polymerization of 60 percent piperylene, 10 percent isoprene, 5percent cyclopentadiene, 15 percent 2-methyl-2-butene and about 10percent dimer, as taught in U.S. Pat. No. 3,577,398. Other adhesionpromoting resins which are also useful in compositions of the presentinvention include hydrogenated rosins, esters of rosins, polyterpenes,terpene phenol resins and polymerized mixed olefins, lower softeningpoint resins and liquid resins. An example of a liquid resin isRegalrez® 1018 resin (a hydrogenated pure monomer resin) from Hercules.The amount of adhesion promoting resin employed varies from 0 to 400parts by weight per 100 parts rubber (phr--the term "rubber" refers tothe block copolymer). The selection of the particular tackifying resinis, in large part, dependent upon the specific polymer employed in therespective adhesive or sealant composition.

The compositions of the present invention may contain plasticizers orcompounding oils or organic or inorganic pigments and dyes. Optionalcomponents are stabilizers which inhibit or retard heat degradation,oxidation, skin formation and color formation. Various types of fillersand pigments can be included in the robber compound or adhesive/sealantformulation. A wide variety of fillers can be used including calciumcarbonate, clays, talcs, silica, zinc oxide, titanium dioxide and thelike. Polyolefin resins such as polypropylene, polyethylene copolymersof ethylene/octene or ethylene/hexene can also be used.

EXAMPLES

The following examples include masterbatches made with a high molecularweight PPE and an endblock resin and a hydrogenated block copolymer of avinyl aromatic hydrocarbon and a conjugated diene as well asmasterbatches made with the block copolymer and a low molecular weightPPE without the endblock resin. For comparative purposes, a blend hasbeen made of a high molecular weight PPE, an endblock compatible resinand the block copolymer. Also provided is a masterbatch blend of a highmolecular weight PPE and a block copolymer (a commercial product)without the endblock compatible resin. Sealant compositions were madefrom all of these blends and the properties of these compositions aredescribed below. The masterbatches were prepared in a Berstroff ZE-25co-rotating intermeshing twin screw extruder using mixing temperaturesof 300° C. and 300 RPM. The sealant formulations were mixed in 1/2 literBaker Perkins Sigma Blade mixer at 177° C. for 5 hours.

Table 1 shows masterbatch formulations mixed on the Berstroff extruderand their properties.

                                      TABLE 1                                     __________________________________________________________________________    Ingredient                             KRATON ® G                         (parts by weight)                                                                      Masterbatch A                                                                           Masterbatch B                                                                           Masterbatch C                                                                           1652                                   __________________________________________________________________________    KRATON ® G                                                                         100       100       100       100                                    1652.sup.1                                                                    PPE (IV = 0.4)                                                                          30                  20                                              PPE (IV = 0.13)     30                                                        ENDEX ® 155               10                                              Irganox 1010                                                                              0.5       0.5       0.5                                           Peak in Tan Delta                                                                      No apparent peak                                                                        155       155        95                                    value (C) at 10HZ                                                             Dynamic viscosity                                                                      48,000    26,000    26,000    25,000                                 in poise at 200° C.                                                    and 100                                                                       radians/sec                                                                   Appearance                                                                             Amber colored                                                                           Clear amber pellet                                                                      Clear amber pellet                                                                      Clear                                           pellets with a      slightly lighter in                                       slight haze         color than the                                                                other blends                                     __________________________________________________________________________     .sup.1 A hydrogenated styrenebutadiene-styrene block copolymer with a         molecular weight of 53,000.                                              

The masterbatches were characterized using a Rheometrics MechanicalSpectrometer Model 800 and a rectangular torsional bar geometry(Thickness=251 mm, Width=2.5 mm, Length-45.25 mm). A dynamicfrequency/temperature sweep procedure was utilized at 10 and 100rad/sec, with a step of 10° C./minute. The tan delta value is the ratioof the loss and stored energy G"/G' in the dynamic experiment. The tandelta value will exhibit a maximum at the temperature at which thestyrene domains of the block copolymer experiences a glass transition.The dynamic viscosity is a measure of the viscosity of the sample at agiven temperature.

As can be seen from Table 1, lowering the IV or molecular weight of thePPE increases the compatibility with the endblock as manifested by avery clear tan delta peak and at the same time reduces the viscosity ofthe blend significantly. Surprisingly, the same thing can beaccomplished by adding the endblock resin ENDEX® 155 to a high molecularweight PPE in the masterbatch in the proportions shown above. Theclarity of the PPE/ENDEX®/KRATON® G1652 blend was also a very goodindication of good compatibility.

The masterbatches were then mixed into sealant formulation theproportions shown in Table 2.

                                      TABLE 2                                     __________________________________________________________________________    Ingredient                                                                    (parts by weight)                                                                       Sealant A                                                                           Sealant B                                                                           Sealant C                                                                           Sealant D                                                                           Sealant E                                   __________________________________________________________________________    Masterbatch A                                                                           130                                                                 Masterbatch B   130                                                           Masterbatch C         130                                                     KRATON ® G1652          100   100                                         ENDEX ® 155                    30                                         Regalrez ® 1018                                                                     250   250   250   250   250                                         Properties                                                                    Brookfield                                                                              12,500                                                                              24,000                                                                              11,600                                                                              2,300 2,700                                       Viscosity (177° C.)                                                    Slump Temp (°C.)                                                                 105   140   100   <70   <70                                         Appearance                                                                              Amber Amber Light Clear --                                                    and   color and                                                                           amber and                                                         opaque                                                                              hazy  opaque                                                  __________________________________________________________________________

A Brookfield Viscometer model RVTD and spindle 29 was used to measurethe viscosity at 177° C. To measure the slump temperature, the sealantformulations were poured hot and allowed to solidify in metal channelswith the following dimensions: 2.0 cm wide, by 2.5 cm high, and 1.5 cmdeep. The channels were placed vertically in an oven and the temperaturewas raised in 5° C. increments, allowing the sample to equilibrate for10 minutes at each temperature before increasing the temperature again.The slump temperature was the temperature at which the sample moved morethan 3/16 inch in the channel. As can be seen from Table 2, PPE in theformulation significantly improves the slump temperature compared withthe pure ENDEX®155 or the sealant with no endblock resin. This would beexpected since the PPE is significantly increasing the glass transitiontemperature of the endblock. Sealant C made with the masterbatch of highmolecular weight PPE (IV=0.4) and the ENDEX® shows almost the same slumptemperature properties even though there is less PPE in the totalformulation. This would indicate that the endblock resin is useful inincreasing the compatibility and efficiency of the PPE in the system,i.e. less PPE can be used to accomplish the same result.

We claim:
 1. A method for making high service temperature rubbercompounds and hot melt adhesive and sealant compositions by combining apolyphenylene ether resin with an elastomeric block copolymer of a vinylaromatic hydrocarbon and a conjugated diene, which comprises:(a) makinga masterbatch of 2 to 50 phr of a polyphenylene ether having anintrinsic viscosity of 0.3 deciliters per gram or more and 100 phr ofsaid block copolymer by mixing them together with 2 to 30 phr of anendblock compatible resin in a twin screw extruder, and (b) mixing themasterbatch with more of the block copolymer.
 2. The method of claim 1with the additional step of mixing the masterbatch with otherformulating ingredients.
 3. The masterbatch of step (a) of claim
 1. 4.The product of the process of claim 1.